Most commercially produced, packaged foods (including beverages) go through a thermal process to render that particular food safe for consumption. The intensity of this thermal process varies depending on the physical characteristics and chemical composition of the food, the type of packaging, and the shelf life desired. Thermal treatment can be achieved either prior to or after filling the product into the package. For example, low acid foods where product is thermally processed prior to filling into the package can employ vastly different processing systems as compared to product that is thermally processed in-package.
To render a thermally processed food product safe for consumption, the manufacturer needs to know how much heat is applied to the product. This heat treatment can be observed as a function of temperature and time. Product temperature is heated to a certain degree and held at-least this temperature for a prescribed amount of time, thus corresponding to a “lethality” value which is conventionally used in the food industry to standardize and quantify the intensity of a thermal process. With pure liquid foods, such as beverages and broths, the temperature of the product can be measured easily by temperature probes at prescribed locations in a process system. The use of conventional temperature probes, however, is not preferred and is in practice almost impossible when temperature is desired to be measured within particulate foods (i.e., liquid foods with native constituent particles) such as soups. In these circumstances, only the liquid fraction of the particulate food can be monitored for temperature by the use of conventional temperature probes. A distinct challenge arises when temperature measurements of the different native constituent particles in the foods are desired.
In any sterilization process, the goal is to ensure commercial sterility in the product as a whole. When the product is comprised of a homogeneous liquid fraction, measurement can be facilitated by use of conventional temperature probes. On the contrary, when the product is comprised of several different particles suspended in a liquid fraction, such as in a garnished soup, it can be extremely difficult to predict sterility in the product as a whole based on the process data that is readily available in a conventional continuous flow sterilization system. The difficulty arises from the fact that different particle types in the product may heat up differently from the liquid stream, thus abrogating the utility and veracity of temperature probe measurements of the liquid faction as an indicator of particle temperature. Particle residence time distribution in the process system adds to the complexity of ensuring commercial sterility of all components.
Batch blending of products in a kettle or ribbon blender, for example, for soup products containing large particulates, can result in particle distribution issues for several reasons, including insufficient blending time, inappropriate agitator design, inappropriate agitator speed or direction, kettle size and shape, garnish level and size, overall liquid amount, particle density, and liquid viscosity. It can, therefore, be difficult to measure a variety of process conditions of interest such as, for example, the direction, orientation, speed, or temperature of a particle in a mixing vessel. Indeed, direct particle temperature measurement using conventional techniques, such as temperature probes, would be significantly challenged, if at all possible, by the movement of particles during such unit operation. It is, therefore, desirable to further optimize such batch process conditions.
Generally speaking, the temperature of a single particle may not be uniform throughout the whole volume of that particle. For example, the outer surface of the particle can heat faster than the core of the particle because the outer surface of the particle is in direct contact with the liquid fraction. Although this is the case for some conventional operations, where either hot water or steam is used as the heating medium, it may not be the case for thermal operations where the food is heated by other means such as infra-red, microwave, direct solar heating, radiation heating, inductive heating, or resistive heating. In addition to temperature variation within the volume of a single particle, different types of particles will flow at different speeds within the liquid fraction as the entire food volume is being pumped through the process system. The particles that flow faster through the system will be subject to the heat treatment for less time.
Aseptic thermal processing generally involves continuous sterilization of the food material using a suitable heat exchanger. The type of heat exchanger used is dictated by properties of the food material such as, for example, viscosity, particle size, and homogeneity. Some food products, such as juice, milk, and broth are homogeneous products and can be processed in plate heat exchangers. Other food products, such as soups having solid particles, can be processed in heat exchangers that can handle particles, such as tubular heat exchangers. To be able to quantify the thermal process for an aseptic operation, one would need to be able to identify the slowest heating particle at its core by assessing known characteristics of the particles, such as size, thermal conductivity, or density. Once the slowest heating particle has been identified, the temperature of this particle (at its coldest spot) can be known at the entrance and exit of the holding tubes associated with the heating system being used, to ensure proper thermal treatment as measured by a variety of decisional factors such as cook-value, lethality, etc. Currently, the art lacks a system that can monitor process conditions, such as direct temperature of the particles, in at least near real time during a continuous flow thermal treatment.
Food scientists and engineers have been experimenting with various technologies to quantify and validate food manufacturing processes. These conventional attempts can generally be classified in two categories, residence time distribution of different particle components and temperature data of the particle components at critical locations in the system.
U.S. Pat. No. 5,261,282 to Grabowski et al., for example, discloses the use of implanted radio frequency transponders (in the form of RFID chips) to identify the residence times of simulated particles passing through a continuous processing system. U.S. Pat. No. 5,741,979 to Arndt et al. discloses the use of dipole antenna marker implants in the particles and microwave transducer detectors to measure particle residence times. Systems such as these, however, do not provide information pertaining to the temperature of the particles of interest, and cannot provide pertinent temperature process information relating to the slowest heating, fastest moving particle(s) of a system.
Further conventional attempts have been made to either measure only temperature or both temperature and residence time of food particles in a continuous processing system. Magnetic resonance imaging thermometry, such as that disclosed by Kantt et al., “Temperature Mapping of Particles During Aseptic Processing with Magnetic Resonance Imaging”, Journal of Food Science, Volume 63, No. 2 (1998), is a non-obstructing and non-contact method, but is not sufficiently rapid enough to provide in-line real time measurement. Eight seconds were taken to image a single 64×64 cross-sectional temperature map. During this time, however, a considerable quantity of product can pass the detector unmonitored. Thus, the number of cross sections that can be observed is very limited, i.e., the detection of the initial location where the lethal thermal treatment is achieved may not be determined for all possible cases.
Other conventional methodologies, with associated shortcomings, include those implementing thermoresistive implants. One such example of this is the local magnetic temperature measurement approach disclosed in U.S. Pat. No. 5,722,317 to Ghiron et al., which is directed to the use of spherical paramagnetic particles for implants and detector coils around the pipes for sensors. This approach then implements a correlation between falling magnetic field strength and temperature increase to calculate the implant temperature from the signals of three sensor coils. However, the negative correlation between the measured magnetic field and the increasing temperature employed by this approach can cause a non-conservative temperature estimation, i.e., the resulting calculation can indicate a higher temperature than is actually present in the implant. This is due to the fact that magnetic field reduction can be caused by a variety of factors other than temperature increase in the implant, such as obstruction of detection by other materials (e.g., other food particles that are present). Still further, the magnetic thermometry approach can be highly susceptible to electro-magnetic interference, thereby greatly increasing the complexity of data collection or veracity of the collected data.
Another methodology is disclosed in U.S. Pat. No. 7,112,954 to Palazoglu et al., which makes use of the change in the magnetic field strength of two or more magnets attached to each other along the same pole and which are secured in a carrier particle which emulates the properties of a real food particle. The magnets are placed in simple, forced attachment using an adhesive having a specific release temperature. When the adhesive melts, at a prescribed threshold temperature, at least one of the magnets rotates to the opposite pole, thereby creating a detectable change in the magnetic field. The location in the processing system where this change in the magnetic field is detected, for a given magnet pair, is assumed to be the location where the simulated particle temperature reaches the threshold temperature. The shortcoming of this methodology is that similar to the method disclosed by Ghiron et al., a direct temperature measurement is not provided. Rather, only an indirect indication of temperature is provided. Further, the resulting indication of temperature is simply one of being above the predetermined threshold temperature of the adhesive, rather than a direct numerical temperature value. Further, there is not a way of uniquely identifying a magnet pair when multiple magnet pairs are introduced into the system at the same time.
Therefore, there is a need in the art for systems and methods for directly monitoring the particulate temperature of thermally treated heterogeneous fluids having a plurality of constituent food particles.